Many methods have been devised to facilitate the dispensing of dry powder, such as toner used in photocopiers. A chief problem addressed in the prior art is that such powders tend to clump together with the result that the toner cannot be uniformly and predictably dispensed. The solution often used is to agitate the toner which breaks down the clumps and maintains the powder as finely divided particles which will flow like a fluid down an inclined plane. The use of funnel shaped vibrating containers in this manner to facilitate the dispensing of agitated powders is shown for example by Frohbach, et al., in U.S. Pat. No. 3,134,849 issued May 26, 1964 and Stavrakis, et al., in U.S. Pat. No. 2,910,964 issued Nov. 3, 1959. A modified funnel shaped container wherein one side of the container is sloped and one side of the container is vertical has been shown by Tobias in U.S. Pat. No. 4,069,791 issued Jan. 24, 1978. Unfortunately in such modified containers the agitated powder tends to fall irregularly down the vertical side as powder is dispensed.
The devices of Frohbach, et al., Stavrakis, et al., and Tobias use relatively low frequency (60 cps) vibrators such as solenoids to vibrate their toner containers. The suggestion that the use of higher frequencies to drive the toner dispenser might have some utility by producing more finely divided powders was made made by Rozmus in U.S. Pat. No. 4,298,168, column 6, lines 3-7, issued Nov. 3, 1981. Thus, the flow of powder out of a dispenser or down an inclined plane is sensitive to the vibrating frequency of the dispenser or plane. Below a certain frequency depending on the precise physical characteristics of the powder it is very hard to prevent packing and clumping and make the toner behave as a fluid and flow at all. However, it has also been found that above a certain frequency the powder becomes so agitated that clouds of dust are created, and the toner again ceases to behave as a fluid. Thus, for any given toner dispensing system there is a range of values for vibrating the powder so as to make the toner behave as a fluid.
Besides merely making the powder behave as a fluid, it is also desirable that the toner be dispensed at a relatively constant rate. In addition, it is also desirable to spring mount the vibrated dispensing system so that the mechanical vibrations will not be transmitted to adjacent mechanisms. Unfortunately, it has been found that if such a spring mounted dispensing system is driven at higher frequencies above 60 cps in order to create more finely divided powders but still not yet high enough to create clouds of dust, the result is that a substantial change in the flow rate of the toner occurs as it is dispensed and the dispenser empties.